This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-149642, filed May 22, 2000; and No. 2001-026170, filed Feb. 1, 2001, the entire contents of both of which are incorporated herein by reference.
The present invention relates to a single-substrate-processing-film-forming method and a single-substrate-heat-processing apparatus for treating a metal oxide film, such as a tantalum oxide film, in a semiconductor processing system. The term xe2x80x9csemiconductor processxe2x80x9d used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
In order to manufacture semiconductor devices, film formation and pattern etching are repeatedly applied to a semiconductor wafer. As semiconductor devices are becoming more and more highly miniaturized and integrated, demands on film formation have become stricter. For example, very thin insulating films, such as capacitor insulating films and gate insulating films are required to be even thinner and to be more insulating.
Conventionally, silicon oxide films and silicon nitride films are used as the insulating films. In recent years, however, it has been proposed to form the insulating films from materials having even higher dielectric constant and higher insulating properties, such as a metal oxide, e.g., tantalum oxide (Ta2O5). The metal oxide film has an insulation property of high reliability even where it has a small effective film thickness, and can further have a high insulation property by means of a reformation process performed after the film deposition (Jpn. Pat. Appln. KOKAI Publication No. 2-283022).
A metal oxide film of this kind can be deposited by means of MOCVD (Metal Organic Chemical Vapor Deposition), i.e., using a vaporized metal organic compound. To form a tantalum oxide film by means of MOCVD, a metal (tantalum) alkoxide, such as Ta(OC2H5)5 (pentoethoxytantalum: PET) is used as a raw material liquid. The raw material liquid is made to bubble by e.g., nitrogen gas, or vaporized by a vaporizer set at a vaporizing temperature, to be in a gaseous state, and is supplied to a process chamber preset to have a vacuum atmosphere. At the same time, an oxidizing gas, such as oxygen, is supplied to the process chamber. The supplied raw material is decomposed to offer a film forming material on the surface of a semiconductor wafer heated to a process temperature of from about 400 to 500xc2x0 C. With this film forming material, a tantalum oxide (Ta2O5) film is formed on the surface of the semiconductor wafer by means of deposition.
In order to reform the tantalum oxide film, i.e., to improve the insulating property, the wafer is transferred into an atmosphere containing ozone. The ozone is irradiated with UV (ultraviolet) rays emitted from a mercury lamp, so that activated oxygen is generated. The activated oxygen causes organic impurities, such as Cxe2x80x94C bonds, contained in the metal oxide film to be decomposed and dissociated therefrom, thereby reforming the tantalum oxide film. As a reformation process of this kind other than the UV ozone reformation process, there is known a so-called remote plasma reformation process utilizing a plasma generating mechanism, which includes an RF (Radio Frequency) power supply disposed on the ceiling of a process chamber. In the case of the remote plasma reformation process, radicals generated by the plasma generating mechanism flow down into the vacuum process field, thereby reforming the tantalum oxide film. If necessary, the reformed tantalum oxide film is then subjected to a crystallization process, in which the film is exposed to a high temperature to degas it.
FIGS. 14A to 14C are views showing a conventional method of forming a tantalum oxide film as an insulating metal oxide film. First, in a CVD apparatus, a tantalum oxide (Ta2O5) film having a certain thickness is deposited on a semiconductor wafer W (FIG. 14A). In this process, a vaporized metal alkoxide and O2 gas are supplied into a process chamber having a vacuum atmosphere in which the semiconductor wafer W is placed. The process temperature at this time is set at, e.g., about 460xc2x0 C.
Then, the wafer W is transferred to a reforming apparatus and the tantalum oxide film 2 is reformed in this apparatus (FIG. 14B). In the case of a UV ozone process, the wafer W is placed in an atmosphere containing ozone (O3), and UV rays emitted from a UV lamp are radiated onto the ozone above the surface of the wafer W. With the reformation process, the energy of the UV rays and activated oxygen cause organic impurities, such as Cxe2x80x94C bonds and hydrocarbons, contained in the tantalum oxide film 2 to be decomposed and dissociated therefrom, thereby reforming the tantalum oxide film 2. The process temperature of the reformation is set at a temperature of, e.g., about 425xc2x0 C., which is not higher than the crystallization temperature of tantalum oxide, to maintain the non-crystal or amorphous state of the film 2. The reformation may be performed by a remote plasma reformation process using radicals, as described above.
Then, the wafer W is transferred to a heat-processing apparatus and the tantalum oxide film 2 is crystallized in this apparatus (FIG. 14C). In this process, an atmosphere containing oxygen gas, and a process temperature, e.g., not lower than 700xc2x0 C., which is higher than the crystallization temperature of tantalum oxide, are used. With this crystallization annealing process, the tantalum oxide film 2 is compacted in a molecular level, and is planarly uniformed in the film thickness, thereby providing an insulating film having a good insulating property.
In the method shown in FIGS. 14A to 14C, where the UV ozone process is used for the reformation, the insulating property of the tantalum oxide film 2 is occasionally not sufficiently reformed. Where the remote plasma process is used for the reformation, not only generated radicals but also ions and electrons both having high energy, which damage the surface of the wafer, flow into the process field.
Furthermore, in the method shown in FIGS. 14A to 14C, the processing time increases with the square of the increasing rate of the thickness of the tantalum oxide film, in order to reform the entirety of the tantalum oxide film. In other words, the processing time acceleratively increases with an increase in the film thickness. In addition, the method requires three process steps, i.e., deposition, reformation, and crystallization, thereby increasing the number of steps. At the same time, the method requires processing apparatuses corresponding to the process steps, thereby increasing the system cost.
An object of the present invention is to provide a single-substrate-processing-film-forming method and a single-substrate-heat-processing apparatus, which allow a metal oxide film having excellent properties to be formed.
Another object of the present invention is to provide a single-substrate-processing-film-forming method and a single-substrate-heat-processing apparatus, which provide advantages in the process throughput and system cost.
According to a first aspect of the present invention, there is provided a single-substrate-processing-film-forming method comprising the steps of:
performing a deposition process of depositing a film consisting essentially of an amorphous metal oxide on a target substrate by means of CVD; and
performing a reformation process of removing an organic impurity contained in the film,
wherein the reformation process comprises a step of supplying an excited oxygen gas as a reforming gas into a process chamber accommodating the target substrate, while exhausting the process chamber, the reforming gas being set to have a concentration of ions and electrons not more than 105/cm3.
According to a second aspect of the present invention, there is provided a single-substrate-processing-film-forming method comprising the steps of:
performing a deposition process of depositing a film consisting essentially of an amorphous metal oxide on a target substrate by means of CVD; and
performing a reformation process of removing an organic impurity contained in the film,
wherein the deposition process comprises a step of supplying a raw material gas, which offers a metal of the metal oxide by decomposition, and an oxidizing gas into a process chamber accommodating the target substrate, while exhausting the process chamber,
the reformation process comprises a step of supplying an excited oxygen gas as a reforming gas into a process chamber accommodating the target substrate, while exhausting the process chamber, the reforming gas being set to have a concentration of ions and electrons not more than 105/cm3, and
the method comprises a step of performing the deposition process and the reformation process at substantially the same time, by supplying the raw material gas, the oxidizing gas, and the reforming gas into the process chamber at substantially the same time.
According to a third aspect of the present invention, there is provided a single-substrate-processing-film-forming apparatus comprising:
an airtight process chamber configured to accommodate a target substrate having a film consisting essentially of an amorphous metal oxide thereon;
a worktable configured to support a target substrate within the process chamber;
a heater configured to heat the film while the target substrate is placed on the worktable;
an exhaust section configured to exhaust the process chamber; and
a reforming gas supply section configured to supply excited oxygen gas into the process chamber, the excited oxygen gas being used as a reforming gas for performing a reformation process of removing an organic impurity contained in the film, the reforming gas being set to have a concentration of ions and electrons not more than 105/cm3.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.